I have been LC since the beginning of May. My TOM that month was avg in length but a bit shorter as far as menstruation. I am now at the end of my second month of LC and am 13 days late. I also take a med called tenuate dospan which is thought to cause thyroid disturbances. Why type of thyroid problem causes unusually long/late cycles ?

Just going onto an LC way of eating changes lots of things. Insulin and glucagon are "master hormones" and changing them by cutting out simple carbs can change all the other hormones.

Usually, women find that their first cycle may be out of whack when starting Low Carbing. They may skip a period or have an extra long one. Sounds as though you are having a combination. I would not panic but keep on the LC way for the next month and see if things settle back to the old normal or find a new normal. If not, then do go and see your doctor. But most women find that the first 2 months may be 'different' than they are used to.

I have hypothyroidism and I have always been on time. So no worries. I noticed that for some reason since I started Atkins it made my TOM a lot heavier.

Changes in diet messes things up a little at first.